Pollutec Recycling

Logistics Of Supply

Plastic resins are bulk commodities. A naphtha cracker producing ethylene has a typical yearly capacity of 500000 tonnes of ethylene, necessitating about 1.2 Mtonnes of naphtha feedstock! Polymerization to resins is conducted with a somewhat lower capacity, but still at the same order of magnitude, say 150000 tonnes. Engineering plastics are produced at lower capacity, but this lower rank is still far superior to the capacity of the largest feedstock recycling units conceived to date!

The problem with post-consumer plastics is their immense variety and widespread application. One tonne of plastics can be converted into either 20000 two-litre drinks bottles or 120 000 carrier bags! Collecting, sorting, baling, and transporting such numbers of lightweight materials is a tremendous task, with typical cost levels as shown in Table 1.10.

From a dispersed source, such as households, curbside collection, followed by sorting, cleaning, baling, is very expensive. The only way to reduce such cost is to introduce take back systems.

In some cases plastics or rubber are easier to collect. Automobile shredder residue is such a potential source of waste plastics, arising at car shredding plant, as can be seen at the following web site [22]. Solving the collection problem is trivial, since the waste accumulate only at a limited number of plants. However, it is a mix of numerous different resins, with embedded dirt, metal, and glass, and the best way to derive value is to dismantle very large items (bumpers, dashboard, tyres, battery boxes) and mechanically or thermally treat the balance. Automotive shredding residues are at present generally sent to landfill. Ebara developed a fluid bed gasifier with subsequent combustion of the producer gas and melting of entrained dust in a cyclonic combustion chamber. The molten ash is tapped and granulated in a water quench. The demonstration plant at Aomori, Japan, has operated on two lines since March 2000.

Waste from electrical and electronic equipment arises at the sorting plant, where the frame, the printed circuit board PCB, the cathode ray tube, etc. are separated for recycling. The remaining plastics fraction is in part flame-retarded, hence contains brominated and antimony compounds. The number of WEEE recycling plants is growing, so that the logistics are no longer a major problem.

Sources of raw materials, methods of identification and sorting have been reviewed by Buekens [14, 23, 24]. It is remarkable that the general trends have remained largely unchanged over the years, albeit that today there is another attitude regarding waste management priorities and conceivably a much larger choice in automated sorting systems. Still, sorting on the workfloor has remained mainly a manual operation until very recently: the introduction of automated scanning and take-back machines created a market for sorters, based on spectral fingerprints of bulk plastic streams. Advances are periodically presented at Identiplast [25].